ESSENTIAL maintenance work to Brookthorpe Bridge between junctions 11a and 12 on the M5 will require narrow lanes on both carriageways from Monday, March 24.

Road users are also advised that a 50 mph speed limit will also be in place for the safety of workers and road users on a half mile section around the bridge, in Stroud Road.

The work, which involves strengthening the foundations of the bridge, is being undertaken as part of a comprehensive package of bridge safety improvements and maintenance.

Project sponsor, Dave Frampton said: “We are really pleased with the progress of this comprehensive programme so far, which is essential to prolong the life of the bridges.

“While we appreciate it is a very full programme we have been able to significantly reduce disruption to road users by undertaking a number of schemes at the same time.”

The foundations of three bridges, including Stroud Road Brookthorpe Bridge, have been attacked by thaumasite, which is a severe form of sulphate attack and can reduce affected concrete to a soft crumbly material.

A number of bridges in the Gloucester area are known to suffer from this and the Highways Agency is managing the repair of these over a number of years.

The work on these three bridges includes exposing the foundations and repairing the areas affected by thaumasite. To keep the bridges safe during the work, extra support will be installed to the bridge decks.

This is the third bridge to be worked on in an 18 month programme. While extensive work is needed to the bridge foundations the scheme has been planned carefully so that all three lanes can be kept open in both directions at all times.

Work on the four bridges between Junctions 10 and 12 will continue until March 2015 and includes strengthening work on the foundations of three bridges and a deck replacement, resurfacing and waterproofing on the fourth bridge.